What Is Amazon SQS? Queue Types and Message Operations

When components in an application communicate directly, there's a risk of data loss if either side goes down. Amazon SQS provides a queue that temporarily holds messages, enabling loose coupling between components. This post covers the basics of SQS — from core concepts to creating queues and sending and receiving messages.

What Is Amazon SQS?

SQS (Simple Queue Service) is a fully managed message queuing service provided by AWS. Producers send messages to a queue, and consumers pull messages from it — allowing components to communicate asynchronously without direct connections.

Because the queue acts as a buffer, messages aren't lost even if the consumer goes down temporarily. You can also scale throughput by running multiple consumers in parallel.

What is Amazon Simple Queue Service? - Amazon Simple Queue Service

Learn about the advantages of using Amazon SQS, such as reliability, scalability, and cost-effective...

docs.aws.amazon.com

Key Features

SQS has several characteristics unique to managed services. Let's take a look at each one.

Feature	Description
Fully managed	AWS handles infrastructure management and redundancy, reducing operational overhead
High availability	Messages are automatically replicated across multiple Availability Zones, eliminating single points of failure
Unlimited throughput	Standard queues support nearly unlimited messages per second (TPS)
Flexible retention	Message retention can be set from 1 minute to 14 days (default: 4 days)
Pay-as-you-go	Charged based on the number of messages sent and received, with 1 million requests free per month

Once a message is received, it becomes invisible to other consumers for a period called the visibility timeout. If the consumer doesn't delete the message after processing, it becomes available again after the timeout — be aware that this can lead to reprocessing.

Amazon SQS visibility timeout - Amazon Simple Queue Service

Learn about visibility timeout, which Amazon SQS uses to prevent consumers from processing a message...

docs.aws.amazon.com

Queue Types

SQS offers two queue types: standard and FIFO. Choose the one that fits your use case.

	Standard Queue	FIFO Queue
Throughput	Nearly unlimited	Up to 3,000 TPS (with batching)
Message ordering	Best-effort (not guaranteed)	Strictly preserves FIFO order
Duplicate delivery	Occasionally possible	No duplicates
Use cases	Log aggregation, notifications, bulk processing	Order processing, payments, inventory updates

Standard queues prioritize throughput, so message ordering isn't guaranteed and the same message may occasionally be delivered more than once. Design your consumers to be idempotent (producing the same result when processing a message multiple times) to handle this safely.

FIFO queues guarantee message ordering and deduplication, but come with throughput limits. Queue names must end with .fifo.

Amazon SQS queue types - Amazon Simple Queue Service

Offers comprehensive information about different types of Amazon SQS queues, including FIFO queues, ...

docs.aws.amazon.com

Dead-Letter Queues

A dead-letter queue (DLQ) is a mechanism that moves messages to a separate queue when they repeatedly fail to be processed.

When a consumer fails to process a message and doesn't delete it, the message becomes available again after the visibility timeout. If it exceeds the configured maximum receive count (maxReceiveCount), it's automatically moved to the DLQ. Inspecting and reprocessing DLQ messages makes it easier to track problematic ones.

The SQS console also provides a "DLQ Redrive" feature to move messages from the DLQ back to the original queue.

Using dead-letter queues in Amazon SQS - Amazon Simple Queue Service

Learn about dead-letter queues, which serve as targets for messages that fail processing, aiding in ...

docs.aws.amazon.com

Try SQS with the AWS CLI

Let's walk through the basic flow using the AWS CLI — from creating a queue to sending, receiving, and deleting messages.

Create a Queue

Start by creating a standard queue. Specify the queue name with --queue-name.

❯ aws sqs create-queue --queue-name exrecord-queue
{
    "QueueUrl": "https://sqs.us-east-1.amazonaws.com/123456789012/exrecord-queue"
}

Save the URL to a variable for use in subsequent commands.

❯ QUEUE_URL="https://sqs.us-east-1.amazonaws.com/123456789012/exrecord-queue"

Send a Message

Send a message to the queue. Specify the message content as a string with --message-body.

❯ aws sqs send-message \
    --queue-url "$QUEUE_URL" \
    --message-body 'This is a test message from SQS.'
{
    "MD5OfMessageBody": "4b999f2b9ac63a0e8c4a2bea7ae2e12b",
    "MessageId": "ca0330b3-c5e5-44d3-85a4-4062ef5dd0f5"
}

Receive a Message

Retrieve a message from the queue. The received message becomes invisible to other consumers for the duration of the visibility timeout.

❯ aws sqs receive-message --queue-url "$QUEUE_URL"
{
    "Messages": [
        {
            "MessageId": "ca0330b3-c5e5-44d3-85a4-4062ef5dd0f5",
            "ReceiptHandle": "AQEBwJnKyrHigUMZj...",
            "MD5OfBody": "4b999f2b9ac63a0e8c4a2bea7ae2e12b",
            "Body": "This is a test message from SQS."
        }
    ]
}

Delete a Message

Once processing is complete, delete the message from the queue. If you don't delete it, it will be redelivered after the visibility timeout expires.

❯ aws sqs delete-message \
    --queue-url "$QUEUE_URL" \
    --receipt-handle "AQEBwJnKyrHigUMZj..."

Delete the Queue

Delete the queue when it's no longer needed. All messages in the queue will also be deleted, so confirm that processing is complete beforehand.

❯ aws sqs delete-queue --queue-url "$QUEUE_URL"

Summary

• Amazon SQS is a fully managed message queuing service that loosely couples application components
• Standard queues offer nearly unlimited throughput; FIFO queues provide ordering guarantees and deduplication
• During the visibility timeout, a message is hidden from other consumers
• Messages that repeatedly fail processing can be moved to a dead-letter queue for easier tracking and reprocessing